Washington (CNN) -- Defense Secretary Robert Gates is expected to leave his post in the spring of 2011, a senior administration source told CNN on Monday.

A Pentagon spokesman confirmed that Gates wants to retire some time next year. Gates was quoted in an article in the magazine Foreign Policy published Monday saying he wanted to step down before the end of 2011.

Pentagon spokesman Bryan Whitman said references in the article to Gates' desire to retire next year "accurately reflect the secretary's thoughts." "He's not about to walk out the door," Whitman said. "He hopes to leave in 2011."

According to the senior administration official, Gates privately promised President Barack Obama he would not leave the Cabinet in 2010 in order to maintain stability at the Pentagon while more U.S. forces are heading to Afghanistan.

In addition, the senior official said, Gates does not want a potentially difficult confirmation battle for his successor to take place in the presidential election year of 2012.

Gates, who became defense secretary in 2006 under former President George W. Bush, stayed in the post when Obama took office in 2009.

White House spokesman Bill Burton praised Gates for his service, telling reporters Monday that the defense secretary has stayed on the job longer than originally planned.

"He did the president and the nation a great favor by agreeing to stay on longer than he had originally intended, when the president started his administration," Burton said. "The president is greatly thankful for that service."

Burton made clear that Gates would decide when to formally announce his plans.

"It's not a surprise to see him discussing his plans to move on," Burton said.

Gates previously spent almost 27 years in the Central Intelligence Agency, including posts at the White House serving four presidents. Gates also was president of Texas A&M University prior to becoming defense secretary.

Last week, Gates announced a Defense Department reorganization plan intended to cut costs. Asked then how long he intended to stay on the job, Gates said: "I'm going to be here longer than either I or others thought."

Geoff Morrell, the Pentagon press secretary, said circumstances would dictate when Gates actually steps down. Morrell noted Gates is involved in numerous major operations and programs, including budget initiatives, an upcoming review of the war in Afghanistan and the withdrawal of troops from Iraq.

"While he desires to get out in 2011, there's a lot on his plate," Morrell said. "We'll see if this is another example of his responsibility trumping his desires."

Asked if Gates risks becoming a lame-duck administrator as opponents of his budget-cutting plan and other steps wait for him to go, Morrell said exact timing of Gates' departure remains uncertain.

"I don't think anyone would dare -- given his [Gates'] history of firing people -- try to play with fire or drag their feet," Morrell said. "They do so at their own peril. The guy is not afraid to fire people who are not on board."